import java.util.Scanner;

public class Main1636 {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int a=sc.nextInt();
        if (a>10){
            System.out.println(String.format("%.1f",a*2*0.9));
        }else System.out.println(a*2);
    }
}
